When most of us think of a heart attack, we tend to picture the movie version: Someone clutches their arm, drops to the ground, and is rushed to the hospital ASAP. But sometimes—especially for women—the signs can be subtle and seemingly unrelated, such as vomiting. Now, new research from the American Heart Association has found that it’s not uncommon to have a heart attack and not even know it.

According to the study, which was published in the journal Circulation, nearly half of all heart attacks may be “silent,” meaning they occur without symptoms most people would recognize or link to a heart attack. In a silent heart attack, blood flow to the heart muscle is severely reduced or cut off entirely and, unfortunately, they can be as bad as a recognized heart attack.

For the study, researchers analyzed the medical records of nearly 9,500 adults and found that, over nine years, 317 people had silent heart attacks while 386 had heart attacks with clinical symptoms. (Researchers discovered the silent heart attacks through electrocardiograms (EKGs) done after the fact.) While silent heart attacks were more common in men, scientists found that they were more likely to kill women, who tend to write off their symptoms more.

“Silent heart attacks are dangerous because people who have them may not get the proper therapy for the heart attack itself and will not get the proper therapy to help prevent another one or modify the known risk factors for coronary artery disease,” Robert A. Kloner, M.D., Ph.D., director of cardiovascular research at Huntington Medical Research Institutes, tells SELF.

Kloner says it can be easy to miss the symptoms of a silent heart attack because they can mimic other conditions. Those symptoms can be indigestion, shortness of breath, dizziness, fatigue, nausea, weakness, and palpitations. “The symptoms in some patients may seem mild and therefore are not taken that seriously,” he says. “Sometimes there are no symptoms at all.”

Jason Wasfy, M.D., a cardiologist at Massachusetts General Hospital, tells SELF that shortness of breath is a big symptom of a silent heart attack—especially for women. It can come with a general feeling of being unwell or it can go away. However, he says it’s important to get checked if you end up having shortness of breath, just in case, and mention to your doctor that it could be a sign of a heart attack. “In general, when women have heart attacks, the symptoms are less typical and a physician may miss them,” he says.

If you think you may have had a silent heart attack, Weinberg says it’s important to call your doctor. Tests like EKGs and magnetic resonance imaging can be used to see if there’s an area of the heart wall that is thinned, scarred, and not contracting, which would suggest that you’ve had a heart attack. Once doctors know what they’re dealing with, they may prescribe medicine, dietary or lifestyle changes, or even surgery, depending on how bad the attack was.

Luckily, silent heart attacks can be treated, but doctors stress the importance of getting checked out if you suspect something is off. “It’s extremely frightening data,” Weinberg says.